Best heat is cozy heat panels I have 4 hanging on walls.Mine coop is heavily insulated ,however.Temp. Never below 50 degrees even at 15 degrees out.Good for small coops,200 watts each.No fire hazard.Cozy brand,about 38$.Last about 2 years each.Mine are on all winter 24 hours day.They still go outside and don't get sick anymore then others.
Always have visible thermometers to check temperature in coop.Also,they dry up air,so coop has very low humidity.Though mine are cleaned every morning.I only use pine shavings.Vet said hay/straw can lead to crop impaction issues and mites.
My hens are spoiled pets,but I cringe when I see chickens getting frostbite.They lay more eggs too,no long periods without eggs.No lights ever used.
I see you have no screening,Mosquitos will bite them,Nats can kill,by choking them.This is more common then many know.
My run is not screened,but the coops windows are.Very important.
Right now they're air conditioner is running 24 hrs.,way too hot for me and them.They come out but,by afternoon,they peck at coop door to go in,cool off.Chickens with mouth open is too hot.They have plenty of shade too,very important.They still like theyre sandboxes even when it's hot.Nw Illinois ,below zero in winter ,can have 100 s in summer.
I always want them to be comfortable ,clean ,well fed,and happy.They deserve a great life.